package com.algrithom.pointer;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * 15. 三数之和
 */
public class Solution10 {
    
    public static void main(String[] args){
        Solution10 solution10 = new Solution10();
        solution10.threeSum(new int[]{-1,0,1,2,-1,-4});
    }
    
    public List<List<Integer>> threeSum(int[] nums){
        List<List<Integer>> ans = new ArrayList<>();
        int len = nums.length;
        if (len < 3)
            return ans;
        Arrays.sort(nums);
        for (int i = 0; i < len; i++) {
            if (nums[i] > 0)
                break;
            if (i > 0 && nums[i] == nums[i - 1])
                continue;
            int L = i + 1;
            int R = len - 1;
            while (L < R) {
                int sum = nums[i] + nums[L] + nums[R];
                if (sum == 0) {
                    ans.add(Arrays.asList(nums[i],nums[L],nums[R]));
                    while (L < R && nums[L] == nums[L + 1])
                        L++;
                    while (L < R && nums[R] == nums[R - 1])
                        R--;
                    L++;
                    R--;
                } else if (sum < 0)
                    L++;
                else R--;
            }
        }
        return ans;
    }
}
